In concrete slip forming machines used for building roads and the like, it is customary to form joints therein at predetermined intervals. One of the reasons for these joints is to hold adjacent sections of concrete together while at the same time allowing for them to shift to some extent, which occurs during freezing and thawing cycles. These dowel bars are typically inserted all the way across the pavement being formed and generally are aligned with the forward movement of the machine. These joints can be perpendicular to the slab and to the direction of forward movement of the machine or they can extend across the strip of concrete being formed at an angle thereto, which is commonplace in present day road construction so that each set of tires of a vehicle does not hit the joint at precisely the same time, thereby lessening the thumping problem that often occurs when the concrete joints are perpendicular to the direction of the movement of the vehicle traveling thereon.
The aforementioned concrete slip forming machines have for many years used dowel bar insertion mechanisms thereon, for example like those shown in U.S. Pat. Nos. 4,798,495 and 4,799,820, both by Laeuppi, et al., both of which are incorporated herein by reference.
Conventional dowel bar inserting equipment is attached to the frame of a slip forming machine behind the pan, for example as shown in U.S. Pat. No. 5,190,397 to Bengford, which patent is incorporated herein by reference. By utilizing this prior art technology with the dowel bar insertion mechanism being behind the pan, the concrete slab which has already been formed, shaped and smoothed by the pan is disturbed considerably by the insertion of the dowel bars therein, which creates a need for an additional trowel following the dowel bar insertion mechanism. Such a trowel is shown in U.S. Pat. No. 5,061,115 to Godbersen, et al. Also, a vibrating screed or correcting beam precedes the trowel on such a machine.
The need to have this dowel bar inserting apparatus and accompanying trowel mechanism makes it necessary to lengthen the machine by a considerable amount. This additional length creates many problems such a making the machine more difficult to move and requiring much more time to assemble and disassemble as these machines are moved from one job site to the other. Additionally, on roads that have sharp vertical curves up or down, if the paver is too long, it can extend completely across such a low spot and not be capable of reaching low enough to correctly pave the surface thereunder or it can extend completely across the high spot leaving only a thin layer of concrete. Furthermore, a machine which has a conventional dowel bar inserting thereon and a follow-up trowel mechanism almost always needs to be a four-track machine, which increases the costs of manufacture and use over that of a two-track machine, and also causes the aforementioned problem relating to the difficulty of being able to pave roads which have sharp vertical curves up and down.
U.S. Pat. No. 5,209,602, issued May 11, 1993 to Gary L. Godbersen, solved many of the aforementioned problems. The present invention is an improvement thereto since it has been determined that it is better to form a wide space in the pan than to merely have openings which extend therethrough for inserting dowel bars.
Consequently, there is a need for a method and apparatus for inserting dowel bars on a concrete slip forming machine which will overcome the aforementioned disadvantages of the prior art.